Two mortars also landed inside the heavily protected Green Zone, while a third landed outside.

The area, the site of government ministries and foreign embassies, has frequently been targeted with rocket and mortar fire.

Major-General Qassim Atta, the spokesman for the Iraqi army's Baghdad operations, blamed Wednesday's attack on Baathist supporters, a reference to the political party of Saddam Hussein, the executed former president.

Iraqi authorities have said they are investigating, and Nuri al-Maliki, Iraq's prime minister, has ordered a widespread review of security forces in Baghdad.

Authorities have also detained 10 army and police commanders who were responsible for overseeing security, traffic and intelligence services in the attacked areas.

The attacks came six years to the day after a lorry bomb exploded outside the UN offices at the Canal Hotel killing 22 people.

Speaking to Al Jazeera, Saad Muttalibi, an adviser to Iraq's ministry of national dialogue and reconciliation, said: "This is the continuation of the evil plans of people who cannot see a stable, free Iraq and people with the intention of keeping American forces in Iraq after the agreement that was signed for the Americans to leave.

"I think that this escalation of violence in Iraq is totally unacceptable as it is affecting the ordinary citizens."

'Sectarian loyalties'

Larry Korb, a former US assistant secretary of defence who has advised US President Barack Obama on policy matters related to Iraq, said the attacks suggest that the country's security forces are still not wholly loyal to the central government.

"They [the Iraqi security forces] are still riven by partisan and sectarian loyalties. There are 600,000 [security personnel] - they should be able to provide the security that we had 150,000 Americans to do," he told Al Jazeera.

"It is really a question of whether [Iraqi leaders] have divided the power equitably and whether they have shared the economic resources in a way that people will not want to do [such attacks] in order to upset an order that they think excludes them."

Despite a reduction in violence in recent months, attacks on security forces and civilians remain common in Baghdad and the northern cities of Mosul and Kirkuk.

The number of violent deaths fell by a third last month to 275 from 437 in June, following the pullout of US combat forces from urban areas at the end of the month.